Mild cognitive impairment refers to the transitional state between the cognitive changes of normal aging and the fully developed clinical features of dementia. This topic has received a great deal of attention in the literature in recent years and is being proposed for clinical applications as well. Clinical guidelines, including the original memory-focused criteria and the more recent broadly defined set of criteria, will be presented. The clinical outcome of individuals with mild cognitive impairment will be discussed and several explanations for variability in the literature will be considered. Predictors of progression, including genetic, neuroimaging, biomarker, and clinical characteristics, will be presented, as will the controversies regarding the underlying neuropathology of mild cognitive impairment. The recently completed mild cognitive impairment clinical trials will be discussed and the lessons learned from them translated into recommendations for future investigations. Finally, the clinical utility of mild cognitive impairment, its incorporation into clinical practice, and directions for future research will be proposed.